As a material for terminals and connectors of electric and electronic apparatuses, brass or phosphor bronze has been generally used. However, recently, reductions in size, thickness, and weight of an electronic apparatus such as a cellular phone and a note-type PC have been progressed. Accordingly, terminals and connector parts thereof, which have a small size and a narrow pitch between electrodes, have been used. In addition, in usage in the vicinity of an engine of a vehicle, reliability under harsh conditions at a high temperature is also required. Along with this, from necessity of maintaining electric connection reliability, strength, electrical conductivity, a bending elastic limit, stress relaxation characteristics, bending formability, fatigue resistance, and the like are demanded to be further improved, and thus brass and phosphor bronze may not cope with this demand. As a substitute for brass and phosphor bronze, the present applicant gives attention to a Cu—Mg—P-based copper alloy as described in PTL 1 to PTL 5, and has provided a copper alloy sheet (product name “MSP1”) for terminals and connectors, which has excellent characteristics, high quality, and high reliability, to the market.
PTL 1 discloses a copper alloy thin sheet for producing connectors. The copper alloy thin sheet is composed of a copper alloy having a composition containing 0.3% by mass to 2% by mass of Mg, 0.001% by mass to 0.02% by mass of P, 0.0002% by mass to 0.0013% by mass of C, and 0.0002% by mass to 0.001% by mass of oxygen, the balance being Cu and unavoidable impurities, and having a structure in which oxide particles containing fine Mg having a grain size of 3 μm or less are uniformly distributed in a basis material.
PTL 2 discloses a drawn copper alloy bar stock which barely causes wear to a mold. The drawn copper alloy bar stock contains, in terms of % by weight, 0.1% to 1.0% of Mg, and 0.001% to 0.02% of P, and the balance being Cu and unavoidable impurities. In the bar stock, surface crystal grains have an elliptical shape, and have dimensions in which an average minor axis of the elliptical crystal grains is 5 μm to 20 μm, and a value of average major axis/average minor axis is 1.5 to 6.0. To form the elliptical crystal grains, adjustment is carried out so that an average grain size is maintained within a range of 5 μm to 20 μm at final annealing immediately before final cold rolling, and then a rolling rate at the final cold rolling process is set within a range of 30% to 85%.
PTL 3 discloses a Cu—Mg—P-based copper alloy in which tensile strength and bending elastic limit are highly balanced, and a method of producing the Cu—Mg—P-based copper alloy. The Cu—Mg—P-based copper alloy is a copper alloy bar stock having a composition containing, in terms of % by mass, 0.3% to 2% of Mg, and 0.001% to 0.1% of P, the balance being Cu and unavoidable impurities. In a case where orientations of all pixels in a surface within an area to be measured of the copper alloy bar stock are measured with an EBSD method by a scanning electron microscope equipped with an electron backscatter diffraction image system, and a boundary having an orientation difference of 5° or more between adjacent pixels is defined as a crystal grain boundary, an area ratio of crystal grains having an average orientation difference of less than 4° between all pixels in the crystal grains is 45% to 55% of the measured area, tensile strength is 641 N/mm2 to 708 N/mm2, and a bending elastic limit is 472 N/mm2 to 503 N/mm2.
PTL 4 discloses a Cu—Mg—P-based copper alloy bar stock, and a method of producing the Cu—Mg—P-based copper alloy bar stock. The Cu—Mg—P-based copper alloy bar stock has a composition containing, in terms of % by mass, 0.3% to 2% of Mg, and 0.001% to 0.1% of P, the balance being Cu and unavoidable impurities. In a case where orientations of all pixels in a surface within an area to be measured of the copper alloy bar stock are measured at a step size of 0.5 μm with an EBSD method by a scanning electron microscope equipped with an electron backscatter diffraction image system, and a boundary having an orientation difference of 5° or more between adjacent pixels is defined as a crystal grain boundary, an average value of the average orientation difference between all pixels within a crystal grain in all crystal grains is 3.8° to 4.2°, tensile strength is 641 N/mm2 to 708 N/mm2, a bending elastic limit is 472 N/mm2 to 503 N/mm2, and a stress relaxation rate after a heat treatment at 200° C. for 1000 hours is 12% to 19%.
PTL 5 discloses a copper alloy bar stock and a method of producing the copper alloy bar stock. The copper alloy bar stock has a composition containing, in terms of % by mass, 0.3% to 2% of Mg, and 0.001% to 0.1% of P, the balance being Cu and unavoidable impurities. In a case where orientations of all pixels in a surface within an area to be measured of the copper alloy bar stock are measured at a step size of 0.5 μm with an EBSD method by a scanning electron microscope equipped with an electron backscatter diffraction image system, and a boundary having an orientation difference of 5° or more between adjacent pixels is defined as a crystal grain boundary, an area ratio of crystal grains having an average orientation difference of less than 4° between all pixels in the crystal grains is 45% to 55% of the measured area, an area average GAM of crystal grains present in the measured area is 2.2° to 3.0°, tensile strength 641 N/mm2 to 708 N/mm2, a bending elastic limit is 472 N/mm2 to 503 N/mm2, and fatigue limit under completely reversed plane bending in the number of repetition times of 1×106 is 300 N/mm2 to 350 N/mm2.
In addition, PTL 6 discloses a cheap copper alloy sheet material which is excellent in not only ordinary bending formability but also bending formability after notching while maintaining high electrical conductivity and high strength, and is excellent in stress relaxation resistance characteristics, and a method of producing the copper alloy sheet material. The copper alloy sheet material has a composition containing 0.2% by mass to 1.2% by mass of Mg, and 0.001% by mass to 0.2% by mass of P, and the balance being Cu and unavoidable impurities. When X-ray diffraction intensity of a {420} crystal plane in a sheet surface of the copper alloy sheet material is set as I{420}, and X-ray diffraction intensity of a {420} crystal plane of a pure copper standard powder is set as I0{420}, the copper alloy sheet has a crystal orientation satisfying a relation of I{420}/I0{420}>1.0, and when X-ray diffraction intensity of a {220} crystal plane in a sheet surface of the copper alloy sheet material is set as I{220}, and X-ray diffraction intensity of a {220} crystal plane of the pure copper standard powder is set as I0{220}, the copper alloy sheet has a crystal orientation satisfying a relation of 1.0≦I{220}/I0{220}3.5.